DLM: Trans Fatty Acids (2001)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To investigate dietary trans-fatty acid intake and risk of CHD in women from participants in the Nurses' Health Study.

Inclusion Criteria:

Women without diagnosed CHD, stroke, diabetes or hypercholesterolaemia in 1980.

Exclusion Criteria:
  • Missing data on questionnaires
  • Questionably high or low energy intakes from questionnaires
  • Previously diagnosed angina, MI or stroke
  • Diabetes or ­serum cholesterol.
Description of Study Protocol:
  • Nurses’ Health Study began in 1976 when 121,700 US female RN’s answered questionnaires
  • Every two years for eight years, the women received a follow-up questionnaire to identify new potential risk factors, as well newly diagnosed disease
  • In 1980, food frequency questionnaires (FFQ) were added to assess fat intake including total fat, SFA, MUFA, PUFA and trans-fatty acids. They were asked about the type of margarine used and the types of fat used for frying, baking and at the table.
Data Collection Summary:

Outcome measures: Major coronary heart disease including non-fatal MI and fatal CHD.

Description of Actual Data Sample:
  • 85,095 women had complete data for analysis
  • 431 cases of new CHD (nonfatal MI or death from CHD).
Summary of Results:
  • Women were grouped into five quintiles of intake of energy-adjusted trans fatty acids in grams per day:
    • 1: 2.4g
    • 2: 3.2g
    • 3: 3.9g
    • 4: 4.5g
    • 5: 5.7g
  • After adjustment for age and energy intake, intake of trans-isomers was directly related to the risk of CHD (RR for highest vs. lowest quintile 1.50 [95% CI, 1.12 to 2.00]) (P for trend= 0.001). The association was stronger for 69,181 women whose margarine consumption over the previous 10 years had been stable (RR for highest vs. lowest quintile (1.67 [95% CI,1.05 to 2.66]) (P for trend=0.002).
  • Intakes of foods that are major sources of trans-isomers (hard margarine, cookies, biscuits, cake, white bread) were each significantly associated with ­ risks for CHD
  • Women consuming more than four teaspoons margarine per day were at ­ risk of CHD [RR 1.66 (95% CI, 1.10 to 2.49)] compared to women consuming margarine less than one per month (P for trend = 0.02)
  • These findings support the hypothesis that consumption of partially hydrogenated vegetable oils may contribute to the occurrence of CHD. Our findings must add concern that the practice of partially hydrogenating vegetable oils to produce solid fats may have reduced the anticipated benefits of substituting these oils for highly saturated fats, and instead contributed to the occurrence of CHD.
Author Conclusion:
  • FFQ validated for measure of trans-fatty acids, calculated vs. adipose tissue measurement of trans-fatty acids in 115 females
  • Correlation between calculated and measured amounts in adipose tissue, 0.51.
Funding Source:
Government: NIH
Reviewer Comments:
  • Trans-fatty acids (TFA) are known to increase CHD. It is a now a health issue and in several states it is banned in restaurants and also now in schools.
  • This study results supports and suggest that TFA increase the risk of CHD in women. This is a very well-written paper with a lot of important information.
  • Further RCTs are required to see TFA effects on metabolic risk factors.

 

Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
 
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? N/A
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) N/A
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? N/A
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? N/A
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) N/A
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? Yes
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.6. Were extra or unplanned treatments described? Yes
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? Yes
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? N/A
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? Yes
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? Yes
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes